Re: A proposal to cancel overriding the DEFAULT operator new/delete

http://xushiwei.com/cancel-overriding-the-default-operator-new-delete

* Motivation

I don't think we need to override the DEFAULT operator new/delete.
This makes your code doesn't work well together 3rdparty code (if it
also overrides them).

Why overriding the DEFAULT operator new/delete is bad?

Allowing to override the DEFAULT operator new/delete means the DEFAULT
operator new/delete are special operators. When we have more than one
implementations of an operator, the compiler/linker will report a
redefining error. However, it allows there are two implementations of
the DEFAULT operator new/delete (one of them is implemented as
default). It sounds good. But, This gives a hint that there may have
many implementations of the DEFAULT operator new/delete. When this
happens, the compiler/linker doesn't know what should it do, and it
reports a redefining error. The C++ programmers have to solve such
accidents, especially when they use 3rdparty codes ?? You know, there
are many libraries overriding the DEFAULT operator new/delete. But
unfortunately, they take a risk of conflict with each other.

* Impact on the Standard

Does my proposal break existing code? Yes, it does. But the compilers
of C++0x have a lot of ways to solve this. For example, the compilers
can skip overriding operator new/delete and use the default
implementation. And they can give a warning that reminds programmers
to eliminate outdated codes.

Why do I think to cancel overriding the DEFAULT operator new/delete is
possible? Because overriding the DEFAULT operator new/delete only
change the implementation, not the semantic (the concept). If
implementations changes the semantic of DEFAULT operator new/delete,
they are bad code indeed.

* Proposed Text

I suggest ISO C++ cancel this feature, just like we can't override
operator+ of all C types. That is:

1. You CAN NOT override these operators:

void* operator new(size_t size);
void operator delete(void* p);

2. You CAN override DEFAULT operator new in non global namespace:

namespace foo
{
     void* operator new(size_t size) { ... }
     void operator delete(void* p) { ... }
};

And then you can use new/delete objects as the following:

int* intObj = foo::new int;
foo::delete intObj;

3. You CAN override NON-DEFAULT operator new. Such as:

void* operator new(size_t size, my_allocator& alloc);

4. There is no need to override a NON-DEFAULT operator delete. If you
need to delete objects in special way, just use:

alloc.destroy(obj);

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